Hospital Welcomes Second Set of Rare 'Mono Mono' Twins

Amanda Arnold, 24, gave birth to identical twin daughters Thursday at Akron General Hospital in Akron, Ohio. The girls were monoamniotic or "mono mono," which means they shared an amniotic sac and placenta in the womb. Experts say the rare condition affects roughly one in 10,000 pregnancies.

Dr. John Stewart, director of maternal and fetal medicine at Akron General Hospital, said the chance of two sets of monoamniotic twins being born at the same hospital is "probably in the order of one in a million to one in ten million."

Stewart added that the rare twins are usually scheduled for delivery between 32 to 34 weeks to avoid complications like becoming entangled in each other's' umbilical cords.

"The babies can cut of their blood supply to each other," Stewart told ABC News.

Arnold was hospitalized for five weeks before the delivery so that doctors could monitor the twins' blood supply. She gave birth by C-section at 32 weeks.

While the girls didn't emerge holding hands, Arnold said they gave their lungs a workout with a healthy cry.

"I just got a glance, they were so little," Arnold said of seeing her daughters for the first time.

The girls are being treated at Akron Children's Hospital, where they will remain for several weeks until they grow bigger and stronger.

Arnold said she expects life will be significantly different when the girls finally get to go home.